Solid oxide fuel cell device (“SOFC” below) are fuel cell device which operate at relatively high temperatures, using an oxide ion-conducting solid electrolyte as electrolyte, with electrodes placed on each side thereof, and with fuel gas supplied to one side thereof and oxidizer (air, oxygen, or the like) supplied to the other side thereof.
In such SOFCs, steam or CO2 is produced by the reaction between oxygen ions passed through the oxide ion-conducting solid electrolyte and fuel, thereby generating electrical and thermal energy. The electrical energy is extracted from the SOFC, where it is used for various electrical purposes. At the same time, the thermal energy is transferred to the fuel, the SOFC, the oxidizer, and the like, and is used to raise the temperature thereof.
Laid Open Unexamined Patent 2005-5213 (Patent Document 1) discloses a electrical generating/hot water supplying cogeneration system. In that fuel cell device, a long cell stack is stacked vertically; this is supplied with fuel gas and oxygen-containing gas. These gases react in the cell stack to produce electricity. Fuel gas and oxygen-containing gas not used in the reaction are combusted at the top end portion of the cell stack, and this heat of combustion is used to heat items such as the converter and the cell stack.
Laid Open Unexamined Patent 2009-32555 (Patent Document 2) discloses a fuel cell device. In this fuel cell device, during startup processing a converter for supplying fuel gas and the fuel cell units themselves heat up to a predetermined temperature. Also during startup processing, switching between a partial oxidation reforming method (POX), an autothermal reforming method (ATR), and a steam reforming method (SR) is implemented as the temperature rises within the reformer, thereby reforming the fuel.
Furthermore, in the fuel cell device set forth in JP-A-2009-32555, electrical generation by the cell stack is begun when the cell stack temperature reaches a temperature at which electrical generation can be started. Electrical generation is thus started when the cell stack is sufficiently heated and in a stable state.    Patent Document 1: Laid Open Unexamined Application 2005-5213    Patent Document 2: Laid Open Unexamined Application 2009-32555
However, in fuel cell units in which fuel not used to generate electricity is combusted at one end portion of the fuel cell units, as in the solid oxide fuel cell device disclosed in Laid Open Unexamined Application 2005-5213, the problem arises that in fuel cell units heated by this combustion heat, it is difficult to heat portions which are separated from the fuel cell combustion section. In other words, in fuel cell units in which fuel is combusted at the top end portion of a fuel cell units, as in the solid oxide fuel cell device disclosed in Laid Open Unexamined Application 2005-5213, the problem arises that in the fuel cell units heated by this combustion heat, it is difficult to heat the lower portion of the fuel cell units, and temperature unevenness can easily arise within each fuel cell unit. This temperature unevenness is especially problematic with elongated fuel cell units.
During the interval between the startup of the fuel cell device and the commencement of electrical generation, in fuel cell device wherein fuel supplied to the fuel cell units is combusted to heat the temperature of the fuel cell units to a temperature at which electrical generation can take place, the problem occurs that a long period of time is needed until the temperature state of the fuel cell units is sufficiently stable. In other words, in fuel cell units in which one end portion of the fuel cell units is intensively heated, a long period of time is required until all the fuel cell units heat up sufficiently without any unevenness, meaning that a long period of time is required after startup until electrical generation can commence.
Therefore the present invention has the object of providing a solid oxide fuel cell device capable of commencing electrical generation in a sufficiently stable state while shortening the time required from startup until the start of electrical generation.